Alkaline earth alumino-silicate glass compositions with improved chemical and mechanical durability

ABSTRACT

According to one embodiment, a glass composition may include from 65 mol. % to about 75 mol. % SiO 2 ; from about 6 mol. % to about 12.5 mol. % Al 2 O 3 ; from about 5 mol. % to about 12 mol. % alkali oxide; and from about 2 mol. % to about 7 mol. % CaO. The glass composition may be free from boron and BaO. The glass composition may be susceptible to strengthening by ion-exchange.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication Ser. No. 61/551,133 filed Oct. 25, 2011 and entitled“Alkaline Earth Alumino-Silicate Glass Compositions with ImprovedChemical And Mechanical Durability” and is a divisional of U.S.Non-Provisional patent application Ser. No. 15/664,796 filed Jul. 31,2017 and entitled “Alkaline Earth Alumino-Silicate Glass Compositionswith Improved Chemical and Mechanical Durability”, which is acontinuation of U.S. Non-Provisional patent application Ser. No.14/823,832 filed Aug. 11, 2015 and entitled “Alkaline EarthAlumino-Silicate Glass Compositions with Improved Chemical andMechanical Durability, which is a continuation of U.S. Non-Provisionalpatent application Ser. No. 13/660,141 filed Oct. 25, 2012 and entitled“Alkaline Earth Alumino-Silicate Glass Compositions with ImprovedChemical and Mechanical Durability,” each of which is incorporatedherein in their entireties.

BACKGROUND Field

The present specification generally relates to glass compositions and,more specifically, to chemically durable glass compositions which aresuitable for use in pharmaceutical packaging.

Technical Background

Historically, glass has been used as the preferred material forpackaging pharmaceuticals because of its hermeticity, optical clarity,and excellent chemical durability relative to other materials.Specifically, the glass used in pharmaceutical packaging must haveadequate chemical durability so as to not affect the stability of thepharmaceutical compositions contained therein. Glasses having suitablechemical durability include those glass compositions within the ASTMstandard ‘Type 1A’ and ‘Type 1B’ glass compositions which have a provenhistory of chemical durability.

Although Type 1A and Type 1B glass compositions are commonly used inpharmaceutical packages, they do suffer from several deficiencies.Foremost is the tendency of these glasses to phase separate.Specifically, the glass tends to separate on a fine microscopic scaleinto an alkali borate phase and a silica rich phase. This phaseseparation may be a precursor to the glass flakes and de-laminationphenomena that have been reported in such glasses.

A second deficiency is that the low levels of alkali and alumina in Type1A and Type 1B glass compositions result in only a minimal ability toion exchange and strengthen these glasses. As a result, pharmaceuticalpackages made from Type 1A and 1B pharmaceutical glasses offer poorresistance to damage from mechanical events such as impacts andscratches.

Accordingly, a need exists for glass compositions which are chemicallydurable and susceptible to chemical strengthening by ion exchange foruse in glass pharmaceutical packages and similar applications.

SUMMARY

According to one embodiment, the glass composition may include fromabout 65 mol. % to about 75 mol. % SiO₂; from about 6 mol. % to about12.5 mol. % Al₂O₃; and from about 5 mol. % to about 12 mol. % alkalioxide, wherein the alkali oxide comprises Na₂O and K₂O. The K₂O may bepresent in an amount less than or equal to 0.5 mol. %. The glasscomposition may also include from about 8.0 mol. % to about 15 mol. % ofat least one alkaline earth oxide. The glass composition may besusceptible to strengthening by ion-exchange.

In another embodiment, a glass composition may include from about 67mol. % to about 75 mol. % SiO₂; from about 6 mol. % to about 10 mol. %Al₂O₃; from about 5 mol. % to about 12 mol. % alkali oxide; and fromabout 8 mol. % to about 15 mol. % of at least one alkaline earth oxide.The alkali oxide may include K₂O in an amount less than or equal toabout 0.5 mol. %. The alkaline earth oxide may include at least one ofSrO and BaO. The glass composition may be free from boron and compoundsof boron and phosphorous and compounds of phosphorous. The glasscomposition may be ion exchangeable to a depth of layer greater than orequal to about 15 μm with a corresponding compressive stress greaterthan or equal to about 250 MPa.

In yet another embodiment, a glass article may be formed from glasscompositions including: from about 67 mol. % to about 75 mol. % SiO₂;from about 6 mol. % to about 10 mol. % Al₂O₃; from about 5 mol. % toabout 12 mol. % alkali oxide; and from about 8 mol. % to about 15 mol. %of at least one alkaline earth oxide. The alkali oxide may include Na₂Oand K₂O. K₂O may be present in an amount less than or equal to 0.5 mol.%. The composition may be free from boron and compounds of boron. Theglass article may have at least a class S3 acid resistance according toDIN 12116; a class A1 base resistance according to ISO 695; and a typeHGA1 hydrolytic resistance according to ISO 720.

In yet another embodiment, a glass article may include a compressivestress layer with a compressive stress greater than or equal to about250 MPa and depth of layer greater than or equal to about 15 μm. Theglass article may have a type HGA1 hydrolytic resistance according toISO 720. The glass article may be formed from a glass composition whichis free of boron and compounds of boron and free from phosphorous andcompounds of phosphorous.

Additional features and advantages of the embodiments will be set forthin the detailed description which follows, and in part will be readilyapparent to those skilled in the art from that description or recognizedby practicing the embodiments described herein, including the detaileddescription which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description describe various embodiments and areintended to provide an overview or framework for understanding thenature and character of the claimed subject matter. The accompanyingdrawing is included to provide a further understanding of the variousembodiments, and is incorporated into and constitutes a part of thisspecification. The drawings illustrate the various embodiments describedherein, and together with the description serve to explain theprinciples and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 graphically depicts the ion-exchange properties (compressivestress and depth of layer) for an inventive glass composition and, forpurposes of comparison, Type 1B glass compositions.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of glasscompositions which exhibit improved chemical and mechanical durability.Such glass compositions are suitable for use in various applicationsincluding, without limitation, as pharmaceutical packaging materials.The glass compositions may also be chemically strengthened, therebyimparting increased mechanical durability to the glass. The glasscompositions described herein generally comprise silica (SiO₂), alumina(Al₂O₃), alkaline earth oxides, and alkali oxides (such as Na₂O and K₂O)in amounts which impart chemical durability to the glass composition.Moreover, the alkali oxide present in the glass compositions facilitatechemically strengthening the glass compositions by ion exchange. Variousembodiments of the glass compositions will be described herein andfurther illustrated with reference to specific examples.

The term “softening point,” as used herein, refers to the temperature atwhich the viscosity of the glass composition is 1×10^(7.6) poise.

The term “annealing point,” as used herein, refers to the temperature atwhich the viscosity of the glass composition is 1×10¹³ poise.

The term “CTE,” as used herein, refers to the coefficient of thermalexpansion of the glass composition over a temperature range from aboutroom temperature (RT) to about 300° C.

The term “chemical durability,” as used herein, refers to the ability ofthe glass composition to resist degradation upon exposure to specifiedchemical conditions. Specifically, the chemical durability of the glasscompositions described herein was assessed according to threeestablished material testing standards: DIN 12116 dated March 2001 andentitled “Testing of glass—Resistance to attack by a boiling aqueoussolution of hydrochloric acid—Method of test and classification;” ISO695:1991, entitled “Glass—Resistance to attack by a boiling aqueoussolution of mixed alkali—Method of test and classification”; and ISO720:1985 entitled “Glass—Hydrolytic resistance of glass grains at 121degrees C.—Method of test and classification.” The classificationswithin each standard are described further herein.

The terms “free” and “substantially free,” when used to describe theconcentration and/or absence of a particular constituent component in aglass composition, means that the constituent component is notintentionally added to the glass composition. However, the glasscomposition may contain traces of the constituent component as acontaminant or tramp in amounts of less than 0.01 mol. %.

The glass compositions described herein are alkaline earthalumino-silicate glass compositions which generally include acombination of SiO₂, Al₂O₃, at least one alkaline earth oxide, andalkali oxide including at least Na₂O and K₂O. In some embodiments, theglass compositions may also be free from boron and compounds containingboron. The combination of these components enables a glass compositionwhich is resistant to chemical degradation and is also suitable forchemical strengthening by ion exchange. In some embodiments, the glasscompositions may further comprise minor amounts of one or moreadditional oxides such as, for example, SnO₂, ZrO₂, ZnO, or the like.These components may be added as fining agents and/or to further enhancethe chemical durability of the glass composition.

In the embodiments of the glass compositions described herein, SiO₂ isthe largest constituent of the composition and, as such, is the primaryconstituent of the glass network. SiO₂ enhances the chemical durabilityof the glass and, in particular, the resistance of the glass compositionto decomposition in acid. Accordingly, a high SiO₂ concentration isgenerally desired. However, if the content of SiO₂ is too high, theformability of the glass may be diminished as higher concentrations ofSiO₂ increase the difficulty of melting the glass which, in turn,adversely impacts the formability of the glass. However, additions ofalkali oxide assist in offsetting this effect by decreasing thesoftening point of the glass. In the embodiments described herein, theglass composition generally comprises SiO₂ in an amount greater than orequal to about 65 mol. % and less than or equal to about 75 mol. %. Insome embodiments SiO₂ is present in the glass composition in an amountgreater than or equal to about 67 mol. % and less than or equal to about75 mol. %. In some other embodiments, SiO₂ is present in the glasscomposition in an amount greater than or equal to about 67 mol. % andless than or equal to about 73 mol. %. In each of these embodiments, theamount of SiO₂ present in the glass composition may be greater than orequal to about 70 mol. % or even greater than or equal to about 72 mol.%.

The glass compositions described herein further include Al₂O₃. Al₂O₃, inconjunction with alkali oxides present in the glass compositions such asNa₂O or the like, improves the susceptibility of the glass to ionexchange strengthening. Moreover, additions of Al₂O₃ to the compositionreduce the propensity of alkali constituents (such as Na and K) fromleaching out of the glass and, as such, additions of Al₂O₃ increase theresistance of the composition to hydrolytic degradation. Moreover,additions of Al₂O₃ greater than about 12.5 mol. % may also increase thesoftening point of the glass thereby reducing the formability of theglass. Accordingly, the glass compositions described herein generallyinclude Al₂O₃ in an amount greater than or equal to about 6 mol. % andless than or equal to about 12.5 mol. %. In some embodiments, the amountof Al₂O₃ in the glass composition is greater than or equal to about 6mol. % and less than or equal to about 10 mol. %. In some otherembodiments, the amount of Al₂O₃ in the glass composition is greaterthan or equal to about 7 mol. % and less than or equal to about 10 mol.%.

The glass compositions also include at least two alkali oxides. Thealkali oxides facilitate the ion exchangeability of the glasscomposition and, as such, facilitate chemically strengthening the glass.The alkali oxides also lower the softening point of the glass, therebyoffsetting the increase in the softening point due to higherconcentrations of SiO₂ in the glass composition. The alkali oxides alsoassist in improving the chemical durability of the glass composition.The alkali oxides are generally present in the glass composition in anamount greater than or equal to about 5 mol. % and less than or equal toabout 12 mol. %. In some of these embodiments, the amount of alkalioxides may be greater than or equal to about 5 mol. % and less than orequal to about 10 mol. %. In some other embodiments, the amount ofalkali oxide may be greater than or equal to about 5 mol. % and lessthan or equal to about 8 mol. %. In all the glass compositions describedherein, the alkali oxides comprise at least Na₂O and K₂O. In someembodiments, the alkali oxides further comprise Li₂O.

The ion exchangeability of the glass composition is primarily impartedto the glass composition by the amount of the alkali oxide Na₂Oinitially present in the glass composition prior to ion exchange.Specifically, in order to achieve the desired compressive stress anddepth of layer in the glass composition upon ion exchange strengthening,the glass compositions include Na₂O in an amount greater than or equalto about 2.5 mol. % and less than or equal to about 10 mol. % based onthe molecular weight of the glass composition. In some embodiments, theglass composition may include Na₂O in an amount greater than or equal toabout 3.5 mol. % and less than or equal to about 8 mol. %. In some ofthese embodiments, the glass composition may include Na₂O in an amountgreater than or equal to about 6 mol. % and less than or equal to about8 mol. %.

As noted above, the alkali oxides in the glass composition also includeK₂O. The amount of K₂O present in the glass composition also relates tothe ion exchangeability of the glass composition. Specifically, as theamount of K₂O present in the glass composition increases, thecompressive stress obtainable through ion exchange decreases.Accordingly, it is desirable to limit the amount of K₂O present in theglass composition. In some embodiments, the amount of K₂O is greaterthan 0 mol. % and less than or equal to about 2.5 mol. % by molecularweight of the glass composition. In some of these embodiments, theamount of K₂O present in the glass composition is less than or equal toabout 0.5 mol. % by molecular weight of the glass composition.

As noted above, in some embodiments, the alkali oxide in the glasscomposition further comprises Li₂O. Including Li₂O in the glasscomposition further decreases the softening point of the glass. Inembodiments where the alkali oxide includes Li₂O, the Li₂O may bepresent in an amount greater than or equal to about 1 mol. % and lessthan or equal to about 3 mol. %. In some embodiments, Li₂O may bepresent in the glass composition in an amount which is greater thanabout 2 mol. % and less than or equal to about 3 mol. %. However, insome other embodiments, the glass composition may be substantially freeof lithium and compounds containing lithium.

The alkaline earth oxides present in the composition improve themeltability of the glass batch materials and increase the chemicaldurability of the glass composition. The presence of alkaline earthoxides in the glass composition also reduce the susceptibility of theglass to de-lamination. In the glass compositions described herein, theglass compositions generally include at least one alkaline earth oxidein a concentration greater than or equal to about 8 mol. % or even 8.5mol. % and less than or equal to about 15 mol. %. In some embodiments,the glass composition may comprise from about 9 mol. % to about 15 mol.% of alkaline earth oxide. In some of these embodiments, the amount ofalkaline earth oxide in the glass composition may be from about 10 mol.% to about 14 mol. %.

The alkaline earth oxide in the glass composition may include MgO, CaO,SrO, BaO or combinations thereof. For example, in the embodimentsdescribed herein the alkaline earth oxide may include MgO. In someembodiments, MgO may be present in the glass composition in an amountwhich is greater than or equal to about 2 mol. % and less than or equalto about 7 mol. % by molecular weight of the glass composition, or evengreater than or equal to about 3 mol. % and less than or equal to about5 mol. % by molecular weight of the glass composition.

In some other embodiments, the concentration of MgO in the glasscomposition may be reduced in order to lower the liquidus temperature ofthe glass composition and increase the liquidus viscosity, both of whichimprove the formability of the glass composition. For example, in someembodiments, the concentration of MgO may be greater than 0 mol. % andless than or equal to 3.5 mol. %. In some other embodiments, theconcentration of MgO may be greater than 0 mol. % and less than or equalto 3.0 mol. % or even less than or equal to 2.5 mol. %.

In some embodiments, the alkaline earth oxide also includes CaO. Inthese embodiments, CaO is present in the glass composition in an amountfrom about 2 mol. % to less than or equal to 7 mol. % by molecularweight of the glass composition. In some embodiments, CaO is present inthe glass composition in an amount from about 3 mol. % to less than orequal to 7 mol. % by molecular weight of the glass composition. In someof these embodiments, CaO may be present in the glass composition in anamount greater than or equal to about 4 mol. % and less than or equal toabout 7 mol. %. In some other embodiments, CaO may be present in theglass composition in an amount greater than or equal to about 5 mol. %and less than or equal to about 6 mol. %, such as when CaO issubstituted for MgO in the alkaline earth oxide to decrease the liquidustemperature and increase the liquidus viscosity. In still otherembodiments, CaO may be present in the glass in an amount greater thanor equal to about 2 mol. % and less than or equal to about 5 mol. %,such as when SrO is substituted for MgO in the alkaline earth oxide todecrease the liquidus temperature and increase the liquidus viscosity.

In some embodiments described herein, the alkaline earth oxide furthercomprises at least one of SrO or BaO. The inclusion of SrO reduces theliquidus temperature of the glass composition and, as a result, improvesthe formability of the glass composition. In some embodiments the glasscomposition may include SrO in an amount greater than 0 mol. % and lessthan or equal to about 6.0 mol. %. In some other embodiments, the glasscomposition may include SrO in an amount greater than about 0 mol. % andless than or equal to about 5 mol. %. In some of these embodiments, theglass composition may include greater than or equal to about 2 mol. %and less than or equal to about 4 mol. % SrO, such as when CaO issubstituted for MgO in the alkaline earth oxide to decrease the liquidustemperature and increase the liquidus viscosity. In some otherembodiments, the glass composition may include from about 1 mol. % toabout 2 mol. % SrO. In still other embodiments, SrO may be present inthe glass composition in an amount greater than or equal to about 3 mol.% and less than or equal to about 6 mol. %, such as when SrO issubstituted for MgO in the alkaline earth oxide to decrease the liquidustemperature and increase the liquidus viscosity.

In embodiments where the glass composition includes BaO, the BaO may bepresent in an amount greater than about 0 mol. % and less than about 2mol. %. In some of these embodiments, BaO may be present in the glasscomposition in an amount less than or equal to about 1.5 mol. % or evenless than or equal to about 0.5 mol. %. However, in some otherembodiments, the glass composition is substantially free from barium andcompounds of barium.

In the embodiments of the glass compositions described herein, the glasscompositions generally contain less than about 1 mol. % of boron oroxides of boron, such as B₂O₃. For example, in some embodiments theglass compositions may comprise greater than or equal to about 0 mol. %B₂O₃ and less than or equal to 1 mol. % B₂O₃. In some other embodiments,the glass compositions may comprise greater than or equal to about 0mol. % B₂O₃ and less than or equal to 0.6 mol. % B₂O₃. In still otherembodiments, the glass compositions are substantially free from boronand compounds of boron such as B₂O₃. Specifically, it has beendetermined that forming the glass composition with a relatively lowamount of boron or compounds of boron (i.e., less than or equal to 1mol. %) or without boron or compounds of boron significantly increasesthe chemical durability of the glass composition. In addition, it hasalso been determined that forming the glass composition with arelatively low amount of boron or compounds of boron or without boron orcompounds of boron improves the ion exchangeability of the glasscompositions by reducing the process time and/or temperature required toachieve a specific value of compressive stress and/or depth of layer.

In some embodiments of the glass compositions described herein, theglass compositions are substantially free from phosphorous and compoundscontaining phosphorous including, without limitation, P₂O₅.Specifically, it has been determined that formulating the glasscomposition without phosphorous or compounds of phosphorous increasesthe chemical durability of the glass composition.

In addition to the SiO₂, Al₂O₃, alkali oxides and alkaline earth oxides,the glass compositions described herein may optionally further compriseone or more fining agents such as, for example, SnO₂, As₂O₃, and/or Cl⁻(from NaCl or the like). When a fining agent is present in the glasscomposition, the fining agent may be present in an amount less than orequal to about 1 mol. % or even less than or equal to about 0.5 mol. %.For example, in some embodiments the glass composition may include SnO₂as a fining agent. In these embodiments SnO₂ may be present in the glasscomposition in an amount greater than about 0 mol. % and less than orequal to about 0.30 mol. %.

Moreover, the glass compositions described herein may comprise one ormore additional metal oxides to further improve the chemical durabilityof the glass composition. For example, the glass composition may furtherinclude ZnO or ZrO₂, each of which further improves the resistance ofthe glass composition to chemical attack. In these embodiments, theadditional metal oxide may be present in an amount which is greater thanor equal to about 0 mol. % and less than or equal to about 2.0 mol. %.For example, when the additional metal oxide is ZrO₂, the ZrO₂ may bepresent in an amount less than or equal to about 1.5 mol. %.Alternatively or additionally, the additional metal oxide may includeZnO in an amount less than or equal to about 2.0 mol. %. In someembodiments, ZnO may be included as a substitute for one or more of thealkaline earth oxides. For example, in embodiments where the glasscomposition includes the alkaline earth oxides MgO, CaO and SrO, theamount of MgO may be reduced to decrease the liquidus temperature andincrease the liquidus viscosity, as described above. In theseembodiments, ZnO may be added to the glass composition as a partialsubstitute for MgO, in addition to or in place of at least one of CaO orSrO.

In a first exemplary embodiment, the glass composition may include fromabout 65 mol. % to about 75 mol. % SiO₂; from about 6 mol. % to about12.5 mol. % Al₂O₃; and from about 5 mol. % to about 12 mol. % alkalioxide, wherein the alkali oxide comprises Na₂O and K₂O. The K₂O may bepresent in an amount less than or equal to 0.5 mol. %. The glasscomposition may also include from about 8.0 mol. % to about 15 mol. % ofalkaline earth oxide. The glass composition may be susceptible tostrengthening by ion-exchange.

In this first exemplary embodiment, the SiO₂ may be present in the glasscomposition in a concentration from about 67 mol. % to about 75 mol. %.The Al₂O₃ may be present in the glass composition in a concentrationfrom about 6 mol. % to about 10 mol. %. In some embodiments, theconcentration of Al₂O₃ may be greater than about 7 mol. %.

In this first exemplary embodiment, the glass composition may includeless than about 1 mol. % B₂O₃. Alternatively, the glass composition maybe free from boron and compounds of boron.

The alkaline earth oxide of this first exemplary embodiment may includeat least one of SrO and BaO. When SrO is present, the amount of SrO maybe greater than or equal to about 1 mol. % and less than or equal toabout 2 mol. %. Alternatively, the amount of SrO may be greater than 0mol. % and less than or equal to about 6 mol. %.

The glass composition of this first exemplary embodiment may be freefrom barium and compounds of barium.

The alkali metal oxide in the glass composition of this first exemplaryembodiment may further comprise Li₂O in an amount from about 1 mol. % toabout 3 mol. %. The concentration of the alkali oxide Na₂O in this firstexemplary embodiment may be from about 3.5 mol. % to about 8 mol. %.

The alkaline earth oxide in the glass composition of this firstexemplary embodiment may be present in an amount from about 10 mol. % toabout 14 mol. %. The alkaline earth oxide may include MgO and CaO. WhenMgO is present, the MgO may have a concentration greater than 0 mol. %and less than or equal to 3.5 mol. %.

The glass compositions of this first exemplary embodiment may furtherinclude ZrO₂ in an amount less than or equal to about 1.5 mol. % and/orZnO in an amount less than or equal to about 2.0 mol. %. SnO₂ may alsobe added to the glass compositions of this first embodiment in an amountless than or equal to about 0.3 mol. %. The glass composition may alsobe substantially free from phosphorous and compounds of phosphorous.

The glass composition of the first exemplary embodiment may also have aratio of MgO to the sum of the concentrations of the divalent cations(ΣRO) (MgO:ΣRO) of less than 0.3. Divalent cations RO include thealkaline earth oxides (e.g., MgO, CaO, SrO, BaO), ZnO, and the like.

The glass compositions of this first exemplary embodiment may have atleast a class S3 acid resistance according to DIN 12116 both before andafter ion-exchange strengthening; a class A1 base resistance accordingto ISO 695 both before and after ion-exchange strengthening; and/or atype HGA1 hydrolytic resistance according to ISO 720 before and/or afterion exchange strengthening.

In a second exemplary embodiment, a glass composition may include fromabout 67 mol. % to about 75 mol. % SiO₂; from about 6 mol. % to about 10mol. % Al₂O₃; from about 5 mol. % to about 12 mol. % alkali oxide; andfrom about 8 mol. % to about 15 mol. % of alkaline earth oxide. Thealkali oxide may include K₂O in an amount less than or equal to about0.5 mol. %. The alkaline earth oxide may include at least one of SrO andBaO. The glass composition may be free from boron and compounds of boronand phosphorous and compounds of phosphorous. The glass composition maybe ion exchangeable to a depth of layer greater than or equal to about15 μm with a corresponding compressive stress greater than or equal toabout 250 MPa.

The glass composition of this second exemplary embodiment may furthercomprise SrO. When SrO is present, the amount of SrO may be greater thanor equal to about 1 mol. % and less than or equal to about 2 mol. %.Alternatively, the amount of SrO may be greater than 0 mol. % and lessthan or equal to about 6 mol. %.

The glass composition of this second exemplary embodiment may be freefrom barium and/or compounds of barium.

The alkali metal oxide in the glass composition of this second exemplaryembodiment may further comprise Li₂O in an amount from about 1 mol. % toabout 3 mol. %. The concentration of Na₂O in the glass composition ofthis first exemplary embodiment may be from about 3.5 mol. % to about 8mol. %.

The concentration of Al₂O₃ in the glass composition of this secondembodiment may be greater than or equal to about 7 mol. %.

The alkaline earth oxide in the glass composition of this secondexemplary embodiment may be present in an amount from about 10 mol. % toabout 14 mol. %. The alkaline earth oxide may include MgO and CaO. WhenMgO is present, the MgO may have a concentration greater than 0 mol. %and less than or equal to 3.5 mol. %. In this second exemplaryembodiment, the alkaline earth oxide may include from about 5 mol. % toabout 6 mol. % CaO and from about 2 mol. % to about 4 mol. % SrO.

In this second exemplary embodiment, the glass composition may furtherinclude Li₂O in an amount greater than or equal to 1 mol. % and lessthan or equal to 3 mol. %. Alternatively, the glass composition may befree from lithium and compounds containing lithium. The glasscomposition may also include ZnO in an amount less than or equal to 2.0mol. %. Alternatively, the glass composition may be free from zinc andcompounds containing zinc.

The glass composition of this second exemplary embodiment may includeZrO₂ in an amount less than or equal to about 1.5 mol. %.

The glass composition of the second exemplary embodiment may also have aratio MgO:ΣRO which is less than 0.3.

The glass composition of this second exemplary embodiment may have atleast a class S3 acid resistance according to DIN 12116 both before andafter ion-exchange strengthening; a class A1 base resistance accordingto ISO 695 both before and after ion-exchange strengthening; and/or atype HGA1 hydrolytic resistance according to ISO 720 before and/or afterion exchange strengthening.

In a third exemplary embodiment, a glass article may be formed from theglass composition of exemplary embodiment one or exemplary embodimenttwo. In this third exemplary embodiment, the glass article may be ionexchange strengthened such that the glass article has a compressivestress greater than or equal to about 250 MPa and a depth of layergreater than or equal to about 15 Cpm. The glass article may also have acoefficient of thermal expansion less than or equal to 70×10⁻⁷ K⁻¹.

In a fourth exemplary embodiment, a glass article may include acompressive stress layer with a compressive stress greater than or equalto about 250 MPa and depth of layer greater than or equal to about 15μm. The glass article may have a type HGA1 hydrolytic resistanceaccording to ISO 720. The glass article may be formed from a glasscomposition which is free of boron and compounds of boron and free fromphosphorous and compounds of phosphorous.

In this fourth exemplary embodiment, the glass article may have a classS1 base resistance according to ISO 695. The glass article may also haveleast a class S3 acid resistance according to DIN 2116.

The glass article of this fourth exemplary embodiment may be formed froma glass composition which includes from about 67 mol. % to about 75 mol.% SiO₂; from about 6 mol. % to about 10 mol. % Al₂O₃; from about 5 mol.% to about 12 mol. % alkali oxide; and from about 8.0 mol. % to about 15mol. % of alkaline earth oxide. The alkali oxide may include Na₂O andK₂O. The K₂O may be present in an amount less than or equal to 0.5 mol.%. A ratio MgO:ΣRO in the glass composition is less than 0.3.

In the embodiments described herein, the glass compositions generallyhave softening points of less than about 1040° C. or even less thanabout 950° C. In some embodiments, the softening point of the glasscomposition is less than about 900° C. These lower softening pointsimprove the ease of formability of the glass composition.

In some embodiments described herein, the glass compositions have aliquidus viscosity which is greater than or equal to 85 kP or evengreater than or equal to about 90 kP. In some embodiments, the glasscompositions have liquidus viscosities of greater than 150 kP or evengreater than or equal to 200 kP. Such liquidus viscosities can beobtained by decreasing the concentration of MgO in the glass compositionand increasing the concentration of one or more of CaO, SrO and ZnO insubstitution. Glass compositions with liquidus viscosities as describedabove are generally suitable for forming 3-dimensional glass shapes,such as glass tubing.

More specifically, in order to provide a glass composition which isreadily formable into 3-dimensional shapes, the molten glass formed fromthe compositions should generally have a liquidus viscosity of greaterthan or equal to 90 kilopoise (kP). It has been determined that glasscompositions with liquidus viscosities of greater than 90 kP can beobtained by controlling the ratio of MgO to the sum of theconcentrations of the divalent cations (ΣRO). Divalent cations includethe alkaline earth oxides (e.g., MgO, CaO, SrO, BaO), ZnO, and the like.Specifically, it has been determined that when MgO:ΣRO is less than0.30, the glass compositions generally have a liquidus viscosity ofgreater than or equal to 90 kP, preferably greater than or equal to 100kP or even greater than or equal to 115 kP. Accordingly, in someembodiments described herein, the ratio MgO:ΣRO is less than 0.3.

In the embodiments described herein the glass compositions have a CTE ofless than about 70×10⁻⁷K⁻¹ or even less than about 60×10⁻⁷K⁻¹. Theselower CTE values improve the survivability of the glass to thermalcycling or thermal stress conditions relative to glass compositions withhigher CTEs.

As noted above, the presence of alkali oxides in the glass compositionfacilitates chemically strengthening the glass by ion exchange. Byvarying the concentration of alkali oxides in the glass, specificallythe concentration of Na₂O in the glass, a wide range of compressivestresses and depth of layer values are possible for various ion-exchangeprocessing conditions. Glass articles formed from the glass compositionsdescribed herein may have compressive stresses greater than or equal toabout 200 MPa or even 250 MPa following ion-exchange strengthening. Forexample, in some embodiments the compressive stress may be from about200 MPa to about 850 MPa. In some other embodiments, the compressivestress may be from about 500 MPa to about 700 MPa. It should beunderstood that the phrase “compressive stress,” as used herein, refersto the compressive stress in the glass at the surface of the glass. Theglass compositions described herein may be ion-exchange strengthened toachieve depth of layers greater than or equal to about 15 jm, such asfrom about 15 m to about 50 m. For example, in some embodiments, thedepth of layer may be greater than or equal to about 25 m and less thanor equal to about 30 μm. The above referenced compressive stresses anddepth of layers may be obtained in some glass compositions describedherein after the glass composition is treated in a salt bath of 100%molten KNO₃ at a temperatures from about 400° C. to about 500° C. for atime period of less than about 30 hours or even less than about 20hours.

As graphically illustrated in FIG. 1, the glass compositions describedherein can be chemically strengthened by ion exchange. Exemplary depthsof layer and the corresponding compressive stress are graphicallydepicted in FIG. 1. Also, for purposes of comparison, the depth of layerand compressive stress obtainable for Type 1B glass are also depicted.As shown in FIG. 1, the glass compositions described herein may be ionexchanged to achieve a much greater compressive stress and depth oflayer than Type 1B glass.

Further, as noted hereinabove, the glass compositions are chemicallydurable and resistant to degradation as determined by the DIN 12116standard, the ISO 695 standard, and the ISO 720 standard.

Specifically, the DIN 12116 standard is a measure of the resistance ofthe glass to decomposition when placed in an acidic solution. In brief,the DIN 12116 standard utilizes a polished glass sample of a knownsurface area which is weighed and then positioned in contact with aproportional amount of boiling 6M hydrochloric acid for 6 hours. Thesample is then removed from the solution, dried and weighed again. Theglass mass lost during exposure to the acidic solution is a measure ofthe acid durability of the sample with smaller numbers indicative ofgreater durability. The results of the test are reported in units ofmass per surface area, specifically mg/dm². The DIN 12116 standard isbroken into individual classes. Class S1 indicates a half weight loss ofup to 0.7 mg/dm²; Class S2 indicates a half weight loss from 0.7 mg/dm²up to 1.5 mg/dm²; Class S3 indicates a half weight loss from 1.5 mg/dm²up to 15 mg/dm²; and Class S4 indicates a half weight loss of more than15 mg/dm².

The ISO 695 standard is a measure of the resistance of the glass todecomposition when placed in a basic solution. In brief, the ISO 695standard utilizes a polished glass sample which is weighed and thenplaced in a solution of boiling 1M NaOH+0.5M Na₂CO₃ for 3 hours. Thesample is then removed from the solution, dried and weighed again. Theglass mass lost during exposure to the basic solution is a measure ofthe base durability of the sample with smaller numbers indicative ofgreater durability. As with the DIN 12116 standard, the results of theISO 695 standard are reported in units of mass per surface area,specifically mg/dm². The ISO 695 standard is broken into individualclasses. Class A1 indicates weight losses of up to 75 mg/dm²; Class A2indicates weight losses from 75 mg/dm² up to 175 mg/dm²; and Class A3indicates weight losses of more than 175 mg/dm².

The ISO 720 standard is a measure of the resistance of the glass todegradation in distilled water. In brief, the ISO 720 standard protocolutilizes crushed grass grains which are placed in contact with 18 MΩwater under autoclave conditions (121° C., 2 atm) for 30 minutes. Thesolution is then titrated colorimetrically with dilute HCl to neutralpH. The amount of HCL required to titrate to a neutral solution is thenconverted to an equivalent of Na₂O extracted from the glass and reportedin g of glass with smaller values indicative of greater durability. TheISO 720 standard is broken into individual types. Type HGA1 isindicative of up to 62 μg extracted equivalent of Na₂O; Type HGA2 isindicative of more than 62 μg and up to 527 μg extracted equivalent ofNa₂O; and Type HGA3 is indicative of more than 527 μg and up to 930 μgextracted equivalent of Na₂O.

The glass compositions described herein have an acid resistance of atleast class S3 according to DIN 12116 with some embodiments having anacid resistance of at least class S2 or even class S1. Further, theglass compositions described herein have a base resistance according toISO 695 of at least class A2 with some embodiments having a class A1base resistance. The glass compositions described herein also have a ISO720 type HGA2 hydrolytic resistance with some embodiments having a typeHGA1 hydrolytic resistance. It should be understood that, when referringto the above referenced classifications according to DIN 12116, ISO 695and ISO 720, a glass composition or glass article which has “at least” aspecified classification means that the performance of the glasscomposition is as good as or better than the specified classification.For example, a glass article which has a DIN 12116 acid resistance of“at least class S2” may have a DIN 12116 classification of either S1 orS2.

The glass compositions described herein are formed by mixing a batch ofglass raw materials (e.g., powders of SiO₂, Al₂O₃, alkali carbonates,alkaline earth carbonates and the like) such that the batch of glass rawmaterials has the desired composition. Thereafter, the batch of glassraw materials is heated to form a molten glass composition which issubsequently cooled and solidified to form the glass composition. Duringsolidification (i.e., when the glass composition is plasticallydeformable) the glass composition may be shaped using standard formingtechniques to shape the glass composition into a desired final form.Alternatively, the glass article may be shaped into a stock form, suchas a sheet, tube or the like, and subsequently reheated and formed intothe desired final form.

The glass compositions described herein may be shaped into glassarticles having various shape forms including, without limitation,sheets, tubes or the like, which can then be reshaped into other glassarticles such as bottles, glass containers, etc. Given the chemicaldurability of the glass composition, the glass compositions describedherein are particularly well suited for use in the formation ofpharmaceutical packages for containing a pharmaceutical composition,such as liquids, powders and the like. For example, the glasscompositions described herein may be used to form vials, ampoules,cartridges, syringe bodies and/or any other glass container for storingpharmaceutical compositions. Moreover, the ability to chemicallystrengthen the glass compositions through ion exchange can be utilizedto improve the mechanical durability of such pharmaceutical packaging.Accordingly, it should be understood that, in at least one embodiment,the glass compositions are incorporated in a pharmaceutical package inorder to improve the chemical durability and/or the mechanicaldurability of the pharmaceutical packaging.

EXAMPLES

The embodiments of glass compositions described herein will be furtherclarified by the following examples.

Table 1 below contains the composition of Comparative Examples 1-3 andInventive Examples A-D. The softening point, CTE, and chemicaldurability of each composition are also listed. Specifically,Comparative Examples 1-3 contained B₂O₃. Removing B₂O₃ from the glasscomposition to improve the chemical durability typically results in acorresponding undesirable increase in the softening point of the glass.In order to counteract this trend in the glass compositions listed inTable 1, B₂O₃ was replaced with alkali oxide, SiO₂, ZrO₂ or combinationsthereof. The SiO₂ and ZrO₂ improve the chemical durability of the glass.Additions of alkali oxide lowered the softening point of the glass by asmuch as 80° C.

TABLE 1 Comparative Examples 1-3 and Inventive Examples A-D Comp. Comp.Comp. Ex. Ex. Ex. Ex. (Mol %) Ex. 1 Ex. 2 Ex. 3 A B C D SiO₂ 70.8 69.969.3 68.3 68.6 67.7 70.8 Al₂O₃ 12.4 12.4 12.4 9 9.3 10.2 7.1 B₂O₃ 1.20.6 1.2 0.6 0 0 0 Na₂O 0 0 0 2.5 2.5 2.5 2.5 K₂O 0 0 0 2.5 2.5 2.5 2.5MgO 5.1 5.1 5.1 5.1 5.1 5.1 5.1 CaO 5.3 5.3 5.3 5.3 5.3 5.3 5.3 SrO 1.43.8 3.8 3.8 3.8 3.8 3.8 BaO 3.8 1.4 1.4 1.4 1.4 1.4 1.4 ZrO₂ 0 1.5 1.51.5 1.5 1.5 1.5 SnO₂ 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Soft pt. 1034 1031 1030952 963 967 953 (° C.) CTE 40 37 37 48 56 56 56 (×10⁻⁷K⁻¹) DIN-121164.33 4.44 5.29 5.38 5.11 8.59 2.12 ISO-695 64.4 25.4 27.2 26.1 22.8 30.024.1

Table 2 shows the composition and properties of inventive Examples E-J.Specifically, the composition of inventive Examples E-J were used toassess the efficacy of further additions of alkali oxide (Na₂O, K₂O,Li₂O) on chemical durability of the glass as well as ion exchangeperformance. As shown in Table 2, alkali oxide additions as high as 11.5mol. % were examined, with slight increases in SiO₂ content to maintainacid durability. The softening points of these glass compositionsdecreased to as low as 870° C. due to the increase in alkali oxidecontent. Moreover, neither the acid nor base resistances of these glasscompositions were adversely impacted by the higher alkali level, withall glasses falling into either the S2 or S3 DIN 12116 classificationand the A1 ISO 695 classification.

TABLE 2 Compositions and Properties of Inventive Examples E-J (Mol %)Ex. E Ex. F Ex. G Ex. H Ex. I Ex. J SiO₂ 70.8 72.3 72.3 71.7 71.7 71.7Al₂O₃ 7.1 7.1 7.1 7.4 7.04 7.4 Li₂O 0 0 1 0 1 1 Na₂O 2.5 2.5 2.5 10 7 10K₂O 2.5 2.5 2.5 0.5 0.5 0.5 MgO 5.1 5.1 4.1 5.1 5.1 5.1 CaO 5.3 5.3 5.34.3 5.3 4.3 SrO 3.8 3.8 3.8 0.5 2 0 BaO 1.4 1.4 1.4 0.5 0 0 ZrO₂ 1.5 0 00 0 0 SnO₂ 0.3 0.3 0.3 0.3 0.3 0.3 Total 5.0 5.0 6.0 (incl. 10.5 8.5(incl. 11.5 (incl. Alkali 1% Li₂O) 1% Li₂O) 1% Li₂O) Anneal pt 721 707660 642 638 637 (° C.) Soft pt. 954 942 900 873 869 869 (° C.) CTE 56.457.4 59.2 69.0 62.9 70.4 (×10⁻⁷K⁻¹) DIN-12116 2.73 1.74 1.66 1.73 1.491.50 ISO-695 20.5 41.9 52.7 69.9 57.7 45.5

The ion exchangeability of inventive Examples E-J were alsoinvestigated. Specifically, samples of the glass compositions ofinventive Examples E-J were ion exchanged in a molten salt bath of 100%KNO₃ for 15 hours at temperatures of 430° C., 440° C., and 475° C.Thereafter, the surface compression and depth of layer were determined.In the examples discussed herein, the compressive stress and DOL valuesare measured values obtained with an FSM instrument, with thecompressive stress value based on the measured stress opticalcoefficient (SOC). The chemical durability of the samples was alsodetermined following ion exchange. The results are reported in Table 3below.

Table 3 shows that the ion exchangeability of the glass compositions isstrongly dependent on the amount of alkali oxide in the composition.Compressive stress values of 200-350 MPa were reached in glasscompositions with alkali oxide levels of 5 mol. % to 6 mol. %.Compressive stress values of 700-825 MPa were reached in glasscompositions with alkali oxide levels of 8.5 mol. % to 11.5 mol. %.Example H had a compressive stress of 817 MPa with a depth of layer of48 microns after ion exchange for 15 hours at 440° C., values which arecomparable to commercially available ion-exchanged damage-tolerantglass.

Table 3 also shows that ion exchange treatment has minimal effect onchemical durability with the exception of the acid durability of severalof the glasses with higher compressive stress values. In theseinstances, the glass mass lost following testing increased by a factorof 20 to 200 compared to corresponding non-ion exchanged glasscompositions. While not wishing to be bound by theory, this result maybe more of a manifestation of chipping of the glass edge during testingdue to high compressive stress rather than actual decreased chemicalresistance from ion exchange.

TABLE 3 Ion Exchange Properties of Examples E-J Ex. E Ex. F Ex. G Ex. HEx. I Ex. J Total Alkali 5.0 5.0 6.0 (incl. 10.5 8.5 (incl. 11.5 (incl.(mol. %) 1% Li₂O) 1% Li₂O) 1% Li₂O) IX 430°-15 hr, 233 MPa, 214 MPa, 325MPa, 750 MPa, 705 MPa, 800 MPa, 100% KNO₃ 13 μm 20 μm 18 μm 28 μm 17 μm26 μm IX 475°-15 hr, 239 MPa, 219 MPa, 333 MPa, 750 MPa, 695 MPa, — 100%KNO₃ 15 μm 21 μm 22 μm 32 μm 21 μm IX 440°-15 hr, — 220 MPa, — 817 MPa,— — 100% KNO₃ 32 μm 48 μm DIN-12116 (IX) 2.74 2.32 30.7 52.5 538 743Repeat 1.31 1.01 3.68 94.3 58.9 55.6 With pre-boil 1.39 1.17 2.59 80.742.0 57.3 ISO-695 (IX) 19.08 48.86 44.78 79.45 64.54 42.91

Table 4 contains the composition and properties of several inventiveexamples of alkaline earth alumino-silicate glass compositions withintermediate amounts of alkali oxides (i.e., from about 5 mol. % toabout 10.5 mol. %). Each of the samples exhibited an acid resistance ofat least class S3 according to the DIN 12116 standard. Each of thesamples also exhibited a base resistance of class A1 according to theISO 695 standard. Test data for the ISO 720 standard was not available.The softening point of these glass compositions was in the range of830−940° C.

Further, the glass compositions of inventive Examples K-R hadcompressive stress values in the range of 350-600 MPa and depth oflayers up to about 50 μm.

TABLE 4 Composition and Properties of Examples K-R (Mol %) Ex. K Ex. LEx. M Ex. N Ex. O Ex. P Ex. Q Ex. R SiO₂ 72.3 72.3 72.3 72.3 71.7 72.271.7 71.7 Al₂O₃ 7.1 7.1 7.1 7.4 7.4 7.4 7.4 7.4 Li₂O 0 0 0 0 0 0 3 1Na₂O 2.5 4.5 5.9 7.7 7.4 10 5 7.2 K₂O 2.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5MgO 5.1 5.1 5.1 6.8 6.5 5.1 5.1 9.1 CaO 5.3 5.3 5.3 4.3 5.5 4.3 5.3 3.3SrO 3.8 3.8 3.8 0.5 1 0.5 2 0 BaO 1.4 1.4 0 0.5 0 0 0 0 SnO₂ 0.3 0.3 0.30.3 0.3 0.3 0.3 .3 Strain Pt. 604 631 628 632 636 635 562 — (° C.)Anneal Pt. 653 680 678 682 686 687 609 — (° C.) Soft Pt. 887 910 913 911916 940 834 — (° C.) CTE 67.5 61.6 61.1 59.5 57.3 58.3 60.9 — (×10⁻⁷K⁻¹)DIN-12116 — 1.94 1.71 1.43 1.62 — — — ISO-695 — 52.3 16.6 52.7 51.6 — —— ISO-720 — — — — — — — — IX — 600 MPa, 610 MPa 522 MPa — — 730 —440°-15 hr, 25 μm 25 μm 15 μm MPa, 100% 13 μm KNO₃ IX — 590 MPa, 600 MPa520 MPa 424 MPa — — — 475°-15 hr, 37 μm 40 μm 22 μm 12 μm 100% KNO₃ IX —497 MPa, 521 MPa 442 MPa 375 MPa — — — 490°-15 hr, 43 μm 49 μm 30 μm 16μm 100% KNO₃

Table 5 contains the composition and properties of several inventiveexamples of alkaline earth alumino-silicate glass compositions whichinclude alkaline earth oxides with reduced amounts of MgO. Specifically,in Examples S-X, MgO in the alkaline earth oxide was replaced with CaOand, in one example, CaO and ZnO, in order to decrease the liquidustemperature and increase the liquidus viscosity of the glass, therebyimproving formability. The amount of MgO in Examples S-X was maintainedbelow about 3 mol. % and the liquidus viscosity of the glass was greaterthan or equal to 90 kP. In these Examples, the glass compositions had anISO 695 base resistance of A1 both before and after ion exchange.Furthermore, Examples S-X each exhibited an ISO 720 hydrolyticresistance of HGA1 after ion exchange (IX) with Example U exhibiting anISO 720 hydrolytic resistance of HGA1 both before (NIX) and after ionexchange.

TABLE 5 Composition and Properties of Examples R-W (Mol %) EX. S EX. TEX. U EX. V EX. W EX. X SiO₂ 72.4 72.3 72.3 72.2 72.4 72.3 Al₂O₃ 7.4 7.47.4 7.3 7.4 7.1 Li₂O 1.5 1.8 1.5 2.3 0 2.0 Na₂O 7.0 6.6 6.6 6.0 8.0 6.9K₂O 0.5 0.5 0.5 0.5 0.5 0.5 MgO 2.6 2.8 2.3 2.6 2.6 2.6 CaO 5.3 5.3 5.85.8 5.3 5.3 SrO 3.3 3.3 2.2 3.3 3.8 3.3 ZnO 0 0 1.4 0 0 0 SnO₂ 0.3 0.30.3 0.3 0.3 0.3 soft pt (° C.) 841 839 852 829 879 822 200P (° C.) 16001596 1615 1593 1628 1584 liquidus vise 145 kP 90 kP 132 kP 100 kP 205 kP87 kP (kP) DIN-12116 (S1 rating <0.70) NIX 0.89 0.75 1.08 1.16 0.99 1.06IX 0.74 1.09 0.94 1.13 1.41 1.06 ISO-695 (A1 rating <75) NIX 45.4 39.142.5 41.7 51.5 45.8 IX 27.3 49.3 52.3 48.5 49.1 48.4 ISO-720 (HGA-1rating <62) NIX 63.7 66.4 61.0 70.5 65.7 73.3 IX 33.6 31.5 35.6 42.539.0 45.2 IX (100% KNO₃) 490° C.-8 hr 642, 27 648, 24 650, 27 640, 22630, 32 620, 25 (MPa, μm) 490° C.-24 hr 563, 46 573, 43 525, 43 574, 38608, 55 606, 46 (MPa, μm)

Table 6 contains the composition and properties of several inventiveexamples of alkaline earth alumino-silicate glass compositions whichinclude alkaline earth oxides with reduced amounts of MgO. Specifically,in Examples AA-EE, MgO in the alkaline earth oxide was replaced with SrOand, in some embodiments, ZnO, in order to decrease the liquidustemperature, increase the liquidus viscosity and improve the formabilityand the chemical durability of the glass. The amount of MgO in ExamplesAA-EE was maintained below about 3.5 mol. % and the liquidus viscosityof the glass was greater than or equal to 200 kP due to the addition ofSrO in conjunction with CaO, ZnO and/or Li₂O. In these Examples, theglass compositions had an ISO 695 base resistance of A1 both before andafter ion exchange. Furthermore, Examples AA-EE each exhibited an ISO720 hydrolytic resistance of HGA1 both before and after ion exchange.

TABLE 6 Composition and Properties of Examples AA-EE (Mol %) AA BB CC DDEE SiO₂ 72.4 724 72.5 72.4 72.5 Al₂O₃ 7.4 7.4 7.6 7.4 7.6 Li₂O 0 0 0 2.02.0 Na₂O 8.0 8.0 9.0 6.0 6.7 K₂O 0.5 0.5 0.5 0.5 0.5 MgO 2.6 2.6 2.6 2.63.1 CaO 4.3 3.3 2.5 2.3 2.3 SrO 4.8 5.8 3.8 4.8 3.3 ZnO 0 0 1.5 2.0 2.0SnO₂ 0.3 0.3 0.3 0.3 0.3 soft pt (° C.) 878 874 878 843 848 200P (° C.)1618 1623 1658 1612 1643 liquidus visc (kP) 400 kP 315 kP 550 kP 200 kP350 kP DIN-12116 (S1 rating <0.70) NIX 1.81 1.56 1.28 1.02 1.11 IX 3.071.34 1.53 2.49 3.66 ISO-695 (A1 rating <75) NIX 51.6 53.4 48.6 40 44.2IX 49.5 52.8 42.3 47.6 56.7 ISO-720 (HGA-1 rating <62) NIX 58.2 59.653.4 48.6 55.3 IX 32.9 39.7 36.2 41.1 43.8 IX (100% KNO₃) 651, 29 626,29 695, 40 673, 21 683, 28 490° C.-8 hr (MPa, μm) 490° C.-24 hr 617, 51601, 49 633, 66 625, 38 630, 49 (MPa, μm)

Accordingly, based on the foregoing examples, it should be understoodthat some of the glass compositions described herein have an ISO 720hydrolytic resistance of HGA1 both before and after ion-exchangestrengthening while other glass compositions have an ISO 720 hydrolyticresistance only after ion-exchange strengthening. While not wishing tobe bound by theory, it is believe that the improvement in the hydrolyticresistance, base resistance, and acid resistance following ion-exchangestrengthening of the glass substrate is due, at least in part, to thecompressive stress imparted to the glass which is believed to limit theremoval of ions from the glass network.

As noted above, in some embodiments, maintaining the ratio MgO:ΣRO inthe glass compositions to be less than 0.3 generally increases theliquidus viscosity of the glass composition to greater than about 90 kPwhich, in turn, improves the formability of the glass composition. Table7 below includes several of the inventive glass compositions describedabove in which the ratio MgO:ΣRO is less than 0.3 and the correspondingliquidus viscosities. Composition FF included 72.3 mol. % SiO₂, 7.1 mol.% Al₂O₃, 2 mol. % Li₂O, 6.9 mol. % Na₂O, 0.5 mol. % K₂O, 2.6 mol. % MgO,5.3 mol. % CaO, 3.3 mol. % SrO, and 0.3 mol. % SnO₂. At high MgO levels(or more precisely, at high activity levels of MgO), the liquidus phaseis forsterite (Mg₂SiO₄), a persistent phase that readily crystallizes athigh temperature during cooling of the melt, resulting in low (<50 kP)liquidus viscosities. It has been found that forsterite formation can bedelayed to lower temperature/higher liquidus viscosity if MgO activityis minimized. It has also been found that MgO activity can be minimizedby maintaining the MgO:ΣRO ratio to <0.30.

TABLE 7 Ratio MgO:ΣRO Liquidus Viscosity Example MgO:ΣRO (kP) S 0.24 145kP T 0.25 90 kP U 0.20 132 kP V 0.20 100 kP X 0.22 205 kP AA 0.22 400 kPBB 0.22 315 kP CC 0.25 550 kP DD 0.22 200 kP EE 0.29 350 kP FF 0.23 145kP

It should now be understood that the glass compositions described hereinexhibit chemical durability as well as mechanical durability followingion exchange. These properties make the glass compositions well suitedfor use in various applications including, without limitation,pharmaceutical packaging materials.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the embodiments describedherein without departing from the spirit and scope of the claimedsubject matter. Thus it is intended that the specification cover themodifications and variations of the various embodiments described hereinprovided such modification and variations come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A glass composition comprising: from 65 mol. % to75 mol. % SiO_(2;) from 6 mol. % to 12.5 mol. % Al₂O₃; from 5 mol. % to12 mol. % alkali metal oxides; and from 2 mol. % to 7 mol % CaO,wherein: a ratio of a concentration of MgO to the sum of theconcentration of divalent cation oxides (MgO:ΣRO) is less than 0.3; theglass composition is free from boron; the glass composition is free fromBaO; and the glass composition is susceptible to strengthening byion-exchange.
 2. The glass composition of claim 1, wherein the glasscomposition comprises from 8.0 mol. % to 15 mol. % alkaline earth metaloxide.
 3. The glass composition of claim 1, wherein the glasscomposition comprises from 10.0 mol. % to 14 mol. % alkaline earth metaloxide.
 4. The glass composition of claim 1, wherein the glasscomposition comprises from 67 mol. % to 75 mol. % SiO_(2.)
 5. A glasscomposition comprising: from 67 mol. % to 75 mol. % SiO_(2;) from 6 mol.% to 12.5 mol. % Al₂O₃; from 5 mol. % to 12 mol. % alkali metal oxides;and from 0 mol. % to 3.5 mol % MgO, wherein: the glass composition isfree from boron; the glass composition is free from BaO; and the glasscomposition is susceptible to strengthening by ion-exchange.
 6. Theglass composition of claim 5, wherein a ratio of a concentration of MgOto the sum of the concentration of divalent cation oxides (MgO:ΣRO) isless than 0.3.
 7. The glass composition of claim 5, wherein the glasscomposition comprises from 0 mol. % to 3.0 mol % MgO.
 8. The glasscomposition of claim 5, wherein the glass composition comprises from 0mol. % to 2.5 mol % MgO.